Hydraulic Fracture Propagation Law Of Composite Rock Considering Stress Disturbance Effect

When hydraulic fracturing is carried out on composite rock reservoir,the stress disturbance fracturing effect is the key factor affecting the hydraulic fracture propagation path at the bedding plane.However,considering the tightness of fracturing test,it is difficult to monitor the dynamic interaction process between hydraulic fracture and bedding plane and the damage of rock bedding plane caused by the disturbance stress field at the fracture tip by the existing technical means,which leads to neglect in most studies This important factor seriously restricts the development of hydraulic fracture propagation mechanism of composite rock materials.This paper focuses on the stress disturbance effect of hydraulic fracturing,using the methods of laboratory test,theoretical analysis and numerical simulation,systematically studies the hydraulic fracture propagation law of composite rock material under different conditions,the meso fracture mechanism of layer material considering the stress disturbance effect,and the influence law of stress disturbance effect on the hydraulic fracture propagation mode at the layer The main innovative achievements are as follows(1)The true triaxial hydraulic fracturing experiment system is used to study the influence of bedding plane on the propagation of hydraulic fractures.The experimental results show that: when the hydraulic fracture propagates through the bedding plane,there is "unconformity" phenomenon in the rock layers on both sides of the bedding plane,which indicates that the propagation of the hydraulic fracture at the bedding plane is discontinuous,and its propagation path is significantly different from that of the continuous symmetrical double wing hydraulic fracture of homogeneous rock material,that is,the existence of the bedding plane significantly affects the propagation path of the hydraulic fracture.Based on the true triaxial hydrofracturing experiment,three modes of hydraulic fracture extension are concluded:(1)mode I: the hydraulic fracture extends completely along the bedding plane until penetrating,and the hydraulic fracture morphology is similar to "t";(2)mode II: the hydraulic fracture morphology is similar to " ? " because of the coexistence of bedding plane extension and cross bedding extension;(3)mode III:the hydraulic fracture extends along the most vertical direction There is no obvious branching and bifurcation in the direction of large principal stress,and the shape is similar to that of "/".(2)It is found that pumping displacement,fracturing mode,layer cementation strength,in-situ stress and other related fracturing conditions have a significant impact on the expansion of hydraulic fractures at the layer.With the increase of pumping displacement and cementing strength,the mode of hydraulic fracture extension at the bedding plane changes from layer extension to through layer extension,and the hydraulic fracture is not easy to turn at the bedding plane;compared with conventional fracturing,the hydraulic fracture opening of cyclic fracturing is lower,and multiple extension modes are easy to appear at the bedding plane;with the increase of principal stress difference,the number of hydraulic fractures in the bedding plane will gradually decrease The direction of the hydraulic fracture gradually approaches to the vertical direction of the minimum principal stress,and the hydraulic fracture surface gradually tends to be flat.(3)The mechanism of disturbance stress-induced fracturing effect of hydraulic fracturing is clarified.Through the analysis of the disturbance stress field inside the test block,the evolution and distribution of stress field around the hydraulic fracture are obtained,and the principle of stress disturbance induced fracturing is revealed.The process and reason of rock material failure in the layer area under the stress disturbance effect are studied,and the influence of stress disturbance induced fracturing effect on the formation is revealed Based on the influence mechanism of hydraulic fracture propagation path and propagation mode,a nonlinear fracture model of disturbed fracture zone is established.(4)The evolution law of layer damage under stress disturbance effect is mastered,the sensitivity test research of stress disturbance effect is carried out,and the evaluation method of hydraulic fracturing stress disturbance effect based on layer damage is established;based on the evaluation index,the damage situation of layer disturbance fracture zone under different pumping displacement,in-situ stress and layer cementation strength is studied;the stress disturbance is revealed The relationship between the stress disturbance effect and the mode of hydraulic fracture extension is obtained,and the control principles and measures of the stress disturbance effect of hydraulic fracture are given according to different construction background.There are 61 figures,19 tables and 83 references in this thesis.